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Communication

Toxic Potential and Long-Term Dynamics of Cyanobacterial Blooms in the Gulf of Gdańsk (Southern Baltic Sea)

by
Agata Błaszczyk
* and
Justyna Kobos
Department of Marine Biology and Biotechnology, Faculty of Oceanography and Geography, University of Gdańsk, al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland
*
Author to whom correspondence should be addressed.
Water 2025, 17(17), 2633; https://doi.org/10.3390/w17172633
Submission received: 24 July 2025 / Revised: 1 September 2025 / Accepted: 3 September 2025 / Published: 6 September 2025
(This article belongs to the Section Oceans and Coastal Zones)
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Abstract

Over the past 15 years, Nodularia spumigena blooms in the Gulf of Gdańsk (southern Baltic Sea) have reached exceptional intensity, accounting for up to 90% of phytoplankton biomass during peak summer periods. Our long-term observations revealed oscillations in blooms intensity, with peak nodularin concentrations (up to 45,000 μg/L) recorded in 2012, 2015, and 2018—the highest levels of this toxin documented to date in both the Baltic Sea and worldwide. An extreme cyanobacterial bloom in 2018, caused by unusually high air and water temperatures, covered almost the whole surface of the Gulf of Gdańsk, causing multi-day closures of bathing areas. During this bloom, high levels of microcystins (up to 6640 μg/L MC-LR) were also detected, as well as the presence of 42 cyanopeptides, mainly anabaenopeptides and spumigins, which were present at concentrations 5–10 times higher than hepatotoxins.

Graphical Abstract

1. Introduction

The large-scale occurrence of diazotrophic cyanobacteria in the Gulf of Gdańsk (southern Baltic Sea) has been reported for several decades [1,2]. Summer blooms are consistently dominated by the cyanobacterium Nodularia spumigena Mertens ex Bornet & Flahault 1888, with additional contributions from Dolichospermum and Aphanizomenon species. These blooms are enhanced by increasing surface water temperatures (>20 °C), windless weather, and low nitrogen/phosphorus ratios (N/P < 16) [3]. Cyanophages can also affect cyanobacteria abundance; however, this phenomenon is still poorly understood [4,5].
The intensive growth of cyanobacteria causes negative effects that are observable in both the ecological sphere and the sanitary conditions of the water bodies. Disturbances in the balance of the Baltic Sea ecosystem are reflected in the intensification of oxygen deficits near the sea bottom, changes in the structure of organisms, and a decrease in biodiversity. Unfortunately, cyanobacterial blooms also significantly reduce the usability of coastal bathing areas and pose a real threat to tourists, especially when they involve species that produce toxic compounds.
The main producer of cyanotoxins in the southern Baltic Sea is the species N. spumigena [6]. Although there are many morphological forms of this species, differing in cell size and shape, all strains studied so far have shown the ability to synthesize the hepatotoxic nodularin. Baltic strains of N. spumigena can produce 11 nodularin analogs, but their quantity and toxicity are lower than the main form of nodularin (NOD) [2]. Nodularin (824 Da) is a pentapeptide that contains several unusual non-proteinogenic amino acids, such as Mdhb (methyldehydrobutyrine) and Adda residue. Other compounds belonging to the hepatotoxin group include microcystins (MCs) (881–1116 Da), cyclic heptapeptides with a structure similar to nodularin. In the Gulf of Gdańsk, cyanobacteria of the Dolichospermum genus are the main producers of microcystins. Apart from nodularin, the Baltic N. spumigena is also a source of several other classes of non-ribosomal oligopeptides, including spumigins (SPU), aeruginosins (AER), and anabaenopeptins (AP) [7]. Spumigins and aeruginosins (461–803 Da) are linear tripeptides and tetrapeptides, while anabaenopeptins (759–956 Da) are cyclic hexapeptides. Many studies have demonstrated the diverse biological activities of the above-mentioned cyanometabolites, including the inhibition of key metabolic pathways, along with their influence on cyanobacterial physiology, which may significantly affect bloom dynamics and reduce phytoplankton biodiversity [8,9,10].
In this study, we summarized 15 years of research on summer cyanobacterial blooms in the Gulf of Gdańsk. We characterized one of the most extensive cyanobacterial blooms recorded in this region, which occurred in 2018. The study includes the assessment of cyanobacterial composition and biomass, as well as chemical analyses of bloom samples to identify known cyanotoxins and other secondary metabolites.

2. Materials and Methods

2.1. Sampling Area

The Gulf of Gdańsk is located in the southeastern part of the Baltic Sea; the water salinity oscillates between 7 and 8 (Practical Salinity Unit), the mean depth is 50 m, and the maximal depth is 118 m. The western subregion of the Gulf of Gdańsk is a unique ecosystem of shallow (up to 3 m) marine waters, which promotes water tourism, including sailing, and wind- and kite-surfing. Moreover, the Gulf of Gdańsk is an area particularly exposed to pollution, due to two reasons: the limited exchange of waters with the open sea, and the influx of the nutrient-contaminated waters of the Vistula River (the second-largest river flowing into the Baltic Sea) [11,12]. In these studies, water bloom samples were collected in the summer seasons of 2010–2024. Bloom sampling was carried out annually, both in the coastal zone of the Gulf of Gdańsk and during research cruises from offshore locations (r/v Oceanograf, University of Gdańsk, Poland). The samples were collected from the surface layer of the water up to three times a week throughout the whole summer season (June–July–August).

2.2. Microscopic Analyses

Samples of phytoplankton were preserved with Lugol’s solution (1%) and stored under cold and dark conditions. Algal/cyanobacterial biomass was determined according to the Utermöhl method, with the use of an inverted microscope (Nikon TMS, Tokyo, Japan) with 200× and 400× magnification [13]. The size of the counting chambers (2 or 10 mL) and the sedimentation time (5 or 24 h) depended on the abundance of phytoplankton. Phytoplankton biomass was calculated using species-specific geometric formulas and standardized size classes, and was performed according to HELCOM recommendations [14,15].

2.3. Extraction and Mass Spectrometry Analyses

Bloom samples were filtered through GF/C filters and extracted with 2 mL 80% ethanol. The extracts were prepared by 15 min bath sonication and followed by incubation at −20 °C for 24 h. Afterwards, samples were vortexed for 1 min and centrifuged at 12,500 rpm for 15 min.
Analyses of bloom extracts were performed using HPLC Agilent 1200 (Agilent Technologies, Santa Clara, CA, USA) coupled to a mass spectrometer QTRAP5500 (Applied Biosystems/MDS Sciex, Marlborough, MA, USA). Chromatographic separation was performed using a Zorbax Eclipse XDB-C18 column (4.6 × 150 mm; 5 μm) (Agilent Technologies, Santa Clara, CA, USA), with the column temperature maintained at 35 °C. The mobile phase was a mixture of 5% acetonitrile in MilliQ water plus 0.1% formic acid (phase A) and 0.1% formic acid in acetonitrile (phase B). The flow rate of the eluent was 600 μL min−1. Positive electrospray ionization was used at ion source temperatures of 550 °C and a voltage of 5.5 keV. Nebulizer and curtain gas pressures were 60 and 20 psi, respectively. The qualitative and quantitative analyses of cyanotoxins were performed using Multiple Reaction Monitoring (MRM) mode. Chromatograms of samples were verified according to MS/MS transitions specific for the cyanotoxin standards.
To determine the oligopeptide profiles in the samples collected in 2018, the analyses were performed using the information-dependent acquisition method (IDA) and enhanced ion product mode (EIP). The percentage composition of oligopeptides was estimated based on the mass peak intensities (MS/MS).
The extrapolation of nodularin content was calculated for a 1 km2 area by 0.1 m water column, according to the formula provided by Kankaanpää et al. (2009) [6].

3. Results and Discussion

3.1. Fifteen-Year Observations of Nodularia spumigena Blooms

In the past, blooms of toxic cyanobacteria in the southern Baltic, particularly in the Gulf of Gdańsk, have been recorded regularly, with intensity and range varying between years. In the 1980s, in July and August, N. spumigena constituted only 17% of the phytoplankton biomass, whereas in the period 1997–2003, the percentage share of this species increased to over 50% [2]. In the last 15 years, the most intense blooms were characterized by a share as high as around 90% of N. spumigena in the phytoplankton biomass. Moreover, in this study, we observed regular oscillations in the concentration of N. spumigena, particularly in the years 2012, 2015, and 2018 (Table 1). Interannual fluctuations in cyanobacterial concentrations, based on satellite data, were also observed in the northern Baltic Sea [16].
Our long-term studies of environmental samples indicate that N. spumigena blooms in the Gulf of Gdańsk are always toxic; however, due to the short duration of the phenomenon (often only several days) and the heterogeneous structure of the phytoplankton community, the number of samples with confirmed toxin presence equals 10–20% of all analyzed samples in the given summer season. Nodularin concentrations measured in samples collected from the Gulf of Gdańsk in 2012, 2015, and 2018 had toxin levels ranging from 35,000 to 45,000 µg/L, which are the highest concentrations of this compound measured to date in the Baltic Sea and in the whole world (Table 1). Taking into consideration the NOD extrapolation over unit area method established by Kankaanpää et al. (2009) [6], the amount of nodularin (3–4 mg/L) during the peak of the bloom could even reach 3–4 tons/km2 in the 0.1 m water layer. Such values exceed typical concentrations reported in natural environments worldwide and highlight the toxic potential of Nodularia spumigena blooms. Fortunately, environmental processes occurring naturally in water, such as bioaccumulation, sorption to sediments, or microbial degradation, can lead to an effective reduction in toxin levels [17]. In other regions of the Baltic Sea, the measured NOD concentrations were not that high. The literature reports indicate that the highest NOD concentration (804 µg/L) was determined in Gotlandsea in 2003 [18].
Nodularin is one of the most potent natural hepatotoxins currently known, and exhibits an LD50 in mice (i.p.) of 30–70 µg/kg b.w. [19]. Symptoms of NOD poisoning include gastrointestinal and hepatic disorders that, in severe cases, may lead to increased vascular permeability, causing blood leakage, which in turn might result in liver damage. Apart from the hepatotoxic activity, nodularin induces the production of reactive oxygen species (ROS), which in turn are the causative factors of oxidative DNA damage, and also exhibits tumor-promoting and—initiating activity [20]. In addition, in the case of cyanobacterial blooms, the overall harmful effect may result from synergic or antagonistic interactions between different bioactive compounds, including known cyanotoxins, but also other cyanobacterial metabolic products present in the marine environment.

3.2. Insights into the Extreme Cyanobacterial Bloom, 2018

In 2018, one of the most intense Nodularia spumigena blooms occurred in the southern Baltic Sea (Table 1 and Table 2). That year, extraordinarily long-lasting and high air (July 20.2 °C) and water temperatures (July 21 °C), combined with a lack of strong wind, caused intense spreading of the cyanobacterial bloom across almost the entire surface of the Gulf of Gdańsk. As a consequence, the bathing sites located on the gulf’s shore were closed for a longer period of time than in previous years. Most bathing sites in the Gulf of Gdańsk were unavailable for tourists for as long as 12 days (Table 1). Intense blooms of cyanobacteria were also recorded in the central and western parts of the Polish coast. Similarly, the occurrence of an exceptionally wide cyanobacterial bloom was observed in the Gulf of Finland, but in contrast, Aphanizomenon flos-aque Ralfs ex Bornet & Flahault 1886 dominated the biomass, and Dolichospermum was more abundant than usual. Nodularia spumigena was present, but in lower quantities. This spectacular phenomenon was reported by global press agencies: “Toxic algae spreads in Baltic waters in biggest bloom in years” [21].
Well before the first signs of the bloom appeared on the coast of the Gulf of Gdańsk, satellite images clearly indicated a subsurface mass occurrence of cyanobacteria [22] (Figure 1). The first peak of cyanobacterial bloom was observed on the 11 July. It was mainly (94%) formed of the long, curled N. spumigena morphotype, typical for the waters of the Gulf of Gdańsk (Table 2). At that time, the concentration of nodularin in coastal waters reached 6750 μg/L. During the second peak of the cyanobacterial bloom (23–25 of July), the phytoplankton community was dominated by long, straight N. spumigena filaments (this morphotype constituted circa 50% of the overall cyanobacterium quantity) that are characteristic of the central part of the Baltic Sea. Then, the concentration of NOD in the coastal zone reached as high as 45,000 μg/L (Table 1 and Table 2). During underwater observations, the cyanobacterial bloom was visible in the water column at depths of up to 55 m [23]. At the same time, diatoms from the species Nitzschia paleacea (Grunow) Grunow 1881 and Cylindrotheca closterium (Ehrenberg) Reimann & J.C. Lewin 1964 appeared in large quantities in phytoplankton biomass. They are a regular component of the phytoplankton community during this time of the year; however, this was the first time they had appeared in such large quantities (12% of phytoplankton biomass). During the last phase of the bloom (29–31 of July), the contribution of cyanobacteria from the Dolichospermum genus significantly increased, reaching up to 50% of the phytoplankton biomass. In the tested samples, anatoxin-a was not detected, but high concentrations of microcystins were determined: 6640 μg/L (MC-LR) and 840 μg/L (MC-RR) (Table 2). MC-LR values exceeded toxin levels recorded in other areas of Europe.
Apart from nodularin and microcystins, three groups of cyanopeptides—spumigins, aeruginosins and anabaenopeptins—were identified. The greatest diversity in this nitrogen-rich cyanopeptide was determined in the late phase of the bloom (29–31 of July) (Figure 2). In total, the structures of 42 compounds were described, including 23 variants of the AP family (Supplementary Materials). Based on the percentage distribution of the total concentrations of cyanopeptides, anabaenopeptins (37–54%) and spumigins (22–46%) constitute the largest share among the analyzed compounds (Figure 2). These two groups of compounds were detected in concentrations 5–10 times greater than the concentration of hepatotoxins. To date, their toxicity remains poorly understood. Spumigins and anabaenopeptins exhibit activity towards serine endopeptidases, such as elastase, trypsin and chymotrypsin, and moreover anabaenopeptins are capable of inhibiting protein phosphatases and zinc-containing metalloexopeptidases, such as carboxypeptidase A (CPA) and carboxypeptidase B (CPB) [10]. According to Lenz et al. (2019) [24], anabaenopeptins exhibit significant toxic effects in the model organism Caenorhabditis elegans at concentrations as low as 10 µg/L, indicating that APs may pose a real risk to aquatic organisms. Research also indicates that anabaenopeptins are involved in defense mechanisms against cyanophages and grazers [25]. According to Sedmak et al. (2008) [8], anabaenopeptins were associated with the collapse of cyanobacterial populations during bloom termination. These oligopeptides may act as molecular triggers, inducing cell lysis mediated by virus-like particles.

3.3. Dominance of Nodularia spumigena in the Southern Baltic Sea

Our studies demonstrate that cyanobacterial blooms in the Gulf of Gdańsk, dominated by Nodularia spumigena, are a source of huge quantities of hepatotoxic nodularin, as well as other bioactive oligopeptides. This potential to produce various metabolites may be related to the ecological and physiological adaptations of Nodularia spumigena, which confer a significant competitive advantage over other cyanobacterial species. N. spumigena successfully develops in brackish waters at low nutrient concentrations. It has developed an advanced system of iron and phosphorus absorption and assimilation. In addition, Popin et al. (2016) [26] identified genes involved in heat shock resistance, osmotic and oxidative stress, antibiotics, toxic compounds, secondary metabolites, and nitrogen metabolism. These findings suggest that N. spumigena has a great capacity to tolerate a wide range of extreme environmental conditions associated with global climate change. Moreover, sedimentary analyses provide evidence for the occurrence of toxic Nodularia spumigena blooms in the Baltic Sea several thousand years ago [27]. It is possible that the present extreme cyanobacterial blooms in the Baltic Sea will leave a footprint on the marine environment for thousands of years to come.

4. Conclusions

Our work summarizes 15 years of studies on summer cyanobacterial blooms in the Gulf of Gdańsk. This research revealed oscillations in the occurrence of large-scale blooms of cyanobacteria; however, they have not been conclusively explained yet. Our findings prove that extremely intense cyanobacterial blooms, such as those in 2012, 2015, and 2018, produce huge amounts of the hepatotoxic nodularin and other bioactive compounds (spumigins, aeruginosins, and anabaenopeptins). While the ecological roles of cyanobacterial metabolites remain incompletely understood, their biotechnological potential is well recognized. Our studies also highlight the possibility of using Baltic cyanobacterial blooms as a natural source of bioactive compounds, offering an alternative to time-consuming laboratory cultivation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w17172633/s1.

Author Contributions

A.B.: Conceptualization, Methodology, Investigation, Visualization, and Writing—Original draft and editing. J.K.: Methodology and Investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This study was supported by funding for the maintenance of scientific and research infrastructure (SPUB), awarded to the University of Gdańsk by the Ministry of Education and Science pursuant to Decision No. 11/526929/SPUB/SP/2022 of 12 August 2022.

Data Availability Statement

All information is included in this manuscript.

Acknowledgments

We would like to thank Hanna Mazur-Marzec for her assistance with the mass-spectrometry analyses. Special thanks go out to Anna Toruńska-Sitarz, Anna Krakowiak, and Katarzyna Sutryk for their helpful suggestions.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Witek, B.; Pliński, M. Occurrence of blue-green algae in the phytoplankton of the Gulf of Gdańsk in the years 1994–1997. Oceanol. Stud. 1998, 3, 77–82. [Google Scholar]
  2. Mazur-Marzec, H.; Krężel, A.; Kobos, J.; Pliński, M. Toxic Nodularia spumigena blooms in the coastal waters of the Gulf of Gdańsk: A ten year survey. Oceanologia 2006, 48, 255–273. [Google Scholar]
  3. Pliński, M.; Mazur-Marzec, M.; Jóźwiak, T.; Kobos, J. The potential causes of cyanobacterial blooms in Baltic Sea estuaries. Oceanol. Hydrobiol. Stud. 2007, 36, 125–137. [Google Scholar] [CrossRef]
  4. Šulčius, S.; Šimoliūnas, E.; Staniulis, J.; Koreivienė, J.; Baltrušis, P.; Meškys, R.; Paškauskas, R. Characterization of a lytic cyanophage that infects the bloom-forming cyanobacterium Aphanizomenon flos-aquae. FEMS Microbiol. Ecol. 2015, 91, 1–7. [Google Scholar] [CrossRef] [PubMed]
  5. Aranda, N.; Bhatt, P.; Ates, N.; Engel, B.A.; Simsek, H. Cyanophage-cyanobacterial interactions for sustainable aquatic environment. Environ. Res. 2023, 229, 115728. [Google Scholar] [CrossRef] [PubMed]
  6. Kankaanpää, H.T.; Sjövall, O.; Huttunen, M.; Olin, M.; Karlsson, K.; Hyvärinen, K.; Sneitz, L.; Härkönen, J.; Sipiä, V.O.; Meriluoto, J. Production and sedimentation of peptide toxins nodularin-R and microcystin-LR in the northern Baltic Sea. Environ. Pollut. 2009, 157, 1301–1309. [Google Scholar] [CrossRef] [PubMed]
  7. Mazur-Marzec, H.; Kaczkowska, M.J.; Błaszczyk, A.; Akcaalan, R.; Spoof, L.; Meriluoto, J. Diversity of peptides produced by Nodularia spumigena from various geographical regions. Mar. Drugs 2012, 11, 1–19. [Google Scholar] [CrossRef] [PubMed]
  8. Sedmak, B.; Carmeli, S.; Elersek, T. “Non-toxic” cyclic peptides induce lysis of cyanobacteria-an effective cell population density control mechanism in cyanobacterial blooms. Microb. Ecol. 2008, 56, 201–209. [Google Scholar] [CrossRef] [PubMed]
  9. Mazur-Marzec, H.; Bertos-Fortis, M.; Toruńska-Sitarz, A.; Fidor, A.; Legrand, C. Chemical and genetic diversity of Nodularia spumigena from the Baltic Sea. Mar. Drugs 2016, 14, 209. [Google Scholar] [CrossRef] [PubMed]
  10. Spoof, L.; Błaszczyk, A.; Meriluoto, J.; Cegłowska, M.; Mazur-Marzec, H. Structures and activity of new anabaenopeptins produced by Baltic Sea cyanobacteria. Mar. Drugs 2016, 14, 8. [Google Scholar] [CrossRef] [PubMed]
  11. Andrulewicz, E.; Witek, Z. Anthropogenic pressure and environmental effects on the Gulf of Gdańsk: Recent Management Efforts. In Baltic Coastal Ecosystems; Schernewski, G., Schiewer, U., Eds.; Central and Eastern European Development Studies; Springer: Berlin/Heidelberg, Germany, 2002; pp. 119–140. [Google Scholar]
  12. Zaborska, A.; Siedlewicz, G.; Szymczycha, B.; Dzierzbicka-Głowacka, L.; Pazdro, K. Legacy and emerging pollutants in the Gulf of Gdańsk (southern Baltic Sea)—loads and distribution revisited. Mar. Pollut. Bull. 2019, 139, 238–255. [Google Scholar] [CrossRef] [PubMed]
  13. Edler, L. Phytoplankton counts. In Results and Analysis of the Intercalibration Experiments; Interim Baltic Marine Environment Protection Commission: Helsinki, Finland, 1979; pp. 1–20. [Google Scholar]
  14. HELCOM. Guidelines for Monitoring of Phytoplankton Species Composition, Abundance and Biomass. 2021. Available online: https://helcom.fi/wp-content/uploads/2020/01/HELCOM-Guidelines-for-monitoring-of-phytoplankton-species-composition-abundance-and-biomass.pdf (accessed on 2 September 2025).
  15. Olenina, I.; Hajdu, S.; Edler, L.; Andersson, A.; Wasmund, N.; Busch, S.; Göbel, J.; Gromisz, S.; Huseby, S.; Huttunen, M.; et al. Biovolumes and Size-Classes of Phytoplankton in the Baltic Sea; Baltic Sea Environment Proceedings No. 106; HELCOM: Helsinki, Finland, 2016. [Google Scholar]
  16. Kahru, M.; Elmgren, R.; Di Lorenzo, E.; Savchuk, O. Unexplained interannual oscillations of cyanobacterial blooms in the Baltic Sea. Sci. Rep. 2018, 8, 6365. [Google Scholar] [CrossRef] [PubMed]
  17. Toruńska, A.; Kotlarska, E.; Mazur-Marzec, H. Biodegradation of nodularin and other nonribosomal peptides by the Baltic bacteria. Int. Biodeterior. Biodegradation 2018, 134, 48–57. [Google Scholar] [CrossRef]
  18. Luckas, B.; Dahlmann, J.; Erler, K.; Gerdts, G.; Wasmund, N.; Hummert, C.; Hansen, P.D. Overview of key phytoplankton toxins and their recent occurrence in the North and Baltic Seas. Environ. Toxicol. 2005, 1, 1–17. [Google Scholar] [CrossRef] [PubMed]
  19. Chen, Y.; Shen, D.; Fang, D. Nodularins in poisoning. Clin. Chim. Acta 2013, 425, 18–29. [Google Scholar] [CrossRef] [PubMed]
  20. Ohta, T.; Sueoka, E.; Iida, N.; Komori, A.; Suganuma, M.; Nishiwaki, R.; Tatematsu, M.; Kim, S.J.; Carmichael, W.W.; Fujiki, H.F. Nodularin, a potent inhibitor of protein phosphatases 1 and 2A, is a new environmental carcinogen in male F344 rat liver. Cancer Res. 1994, 54, 6402–6406. [Google Scholar] [PubMed]
  21. Reuters. Toxic Algae Spreads in Baltic Waters in Biggest Bloom in Years. 2018. Available online: https://www.reuters.com/article/world/toxic-algae-spreads-in-baltic-waters-in-biggest-bloom-in-years-idUSKBN1KM5YD/ (accessed on 22 July 2025).
  22. Swedish Meteorological and Hydrological Institute. Algae Situation-Cyanobacteria. Available online: https://www.smhi.se/data/hav-och-havsmiljo/alger/data-fran-algovervakning (accessed on 2 September 2025).
  23. Turowicz, A. Personal Communication; University of Gdańsk: Gdynia, Poland, 2018. [Google Scholar]
  24. Lenz, K.A.; Miller, T.R.; Ma, H. Anabaenopeptins and cyanopeptolins induce systemic toxicity effects in a model organism the nematode Caenorhabditis elegans. Chemosphere 2019, 214, 60–69. [Google Scholar] [CrossRef] [PubMed]
  25. Rohrlack, T.; Christiansen, G.; Kurmayer, R. Putative antiparasite defensive system involving ribosomal and nonribosomal oligopeptides in cyanobacteria of the genus Planktothrix. Appl. Environ. Microbiol. 2013, 79, 2642–2647. [Google Scholar] [CrossRef] [PubMed]
  26. Popin, R.V.; Rigonato, J.; Abreu, V.A.C.; Andreote, A.P.D.; Silveira, S.B.; Odebrecht, C.; Fiore, M.F. Draft genome assembly of the bloom-forming cyanobacterium Nodularia spumigena strain CENA596 in shrimp production ponds. Genome Announc. 2016, 4, e00466-16. [Google Scholar] [CrossRef] [PubMed]
  27. Cegłowska, M.; Toruńska-Sitarz, A.; Kowalewska, G.; Mazur-Marzec, H. Specific chemical and genetic markers revealed a thousands-year presence of toxic Nodularia spumigena in the Baltic Sea. Mar. Drugs 2018, 16, 102. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Cyanobacteria bloom in the Gulf of Gdańsk, 25 July 2018. (a) Algae map, www.smhi.se; (b) cyanobacteria bloom in the Gulf of Gdańsk, acquired with Sentinel-2A on 25 of July 2018 (© ESA); (c) drone photography of the Gulf of Gdańsk, www.tvbrodnica.pl; (d) Nodularia spumigena bloom in Gdynia, photo: A. Błaszczyk; (e) microscopic pictures of bloom dominants, photo: J. Kobos.
Figure 1. Cyanobacteria bloom in the Gulf of Gdańsk, 25 July 2018. (a) Algae map, www.smhi.se; (b) cyanobacteria bloom in the Gulf of Gdańsk, acquired with Sentinel-2A on 25 of July 2018 (© ESA); (c) drone photography of the Gulf of Gdańsk, www.tvbrodnica.pl; (d) Nodularia spumigena bloom in Gdynia, photo: A. Błaszczyk; (e) microscopic pictures of bloom dominants, photo: J. Kobos.
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Figure 2. Distribution of secondary cyanometabolites (identified by m/z) detected in bloom samples collected on 11, 24, 29, and 31 July 2018 in the Gulf of Gdańsk. The colors indicate different classes of metabolites: brown—aeruginosins, yellow—spumigins, green—nodularin, blue—anabaenopeptins, and dark green—microcystins. The charts illustrate the percentage distribution of total concentrations of cyanometabolites in samples from the Nodularia spumigena bloom in the Gulf of Gdańsk in July 2018.
Figure 2. Distribution of secondary cyanometabolites (identified by m/z) detected in bloom samples collected on 11, 24, 29, and 31 July 2018 in the Gulf of Gdańsk. The colors indicate different classes of metabolites: brown—aeruginosins, yellow—spumigins, green—nodularin, blue—anabaenopeptins, and dark green—microcystins. The charts illustrate the percentage distribution of total concentrations of cyanometabolites in samples from the Nodularia spumigena bloom in the Gulf of Gdańsk in July 2018.
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Table 1. Peaks of Nodularia spumigena blooms in the Gulf of Gdańsk between 2010 and 2024.
Table 1. Peaks of Nodularia spumigena blooms in the Gulf of Gdańsk between 2010 and 2024.
Year DateMax. Cyanobacteria Biomass [mg/L]Max. Concentration of NOD [µg/L]Number of Days with Closed Beaches
Nodularia spumigenaAphanizomenon flos-aquaeDolichospermum spp.
201005/073.70.0020.001201
201130/071538.50.612500
201205/073000n.a.n.a.40,0001
201309/07340.30.2301
201408/07348220.815901–2
201511/08301686535,0001–7
201626/071807152581–7
201701/08110.0222
201824/07325728745,0001–12
201916/073.61.10.033901–7
202019/072988210574651–5
202130/06134978377601
202215/081901563321–4
202310/07789981221001–3
202421/072310.51501–3
Table 2. Characteristics of cyanobacteria bloom in the Gulf of Gdańsk (southern Baltic Sea), July 2018.
Table 2. Characteristics of cyanobacteria bloom in the Gulf of Gdańsk (southern Baltic Sea), July 2018.
Date11 July 201824 July 201829 July 201831 July 2018
Cyanobacteria biomass [mg/L]
Nodularia spumigena847325725971048
Aphanizomenon flos-aquae14282022
Dolichospermum spp.10714531348
Percentage composition of main species in total phytoplankton biomass [%]
Nodularia spumigena—straight164421
Nodularia spumigena—curled94212437
Nodularia spumigena—strongly curled22n.d.n.d.
Dolichospermum spp.1n.d.2950
Aphanizomenon flos-aquae271n.d.
Diatoms: Nitzschia paleacea, Cylindrotheca closteriumn.d.6412
Concentration of NOD [µg/L]675045,00069202760
Concentration of MCs [µg/L]n.d.n.d.5040 (MC-LR)6640 (MC-LR)
840 (MC-RR)
Concentration of Antx-a [µg/L]n.d.n.d.n.d.n.d.
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Błaszczyk, A.; Kobos, J. Toxic Potential and Long-Term Dynamics of Cyanobacterial Blooms in the Gulf of Gdańsk (Southern Baltic Sea). Water 2025, 17, 2633. https://doi.org/10.3390/w17172633

AMA Style

Błaszczyk A, Kobos J. Toxic Potential and Long-Term Dynamics of Cyanobacterial Blooms in the Gulf of Gdańsk (Southern Baltic Sea). Water. 2025; 17(17):2633. https://doi.org/10.3390/w17172633

Chicago/Turabian Style

Błaszczyk, Agata, and Justyna Kobos. 2025. "Toxic Potential and Long-Term Dynamics of Cyanobacterial Blooms in the Gulf of Gdańsk (Southern Baltic Sea)" Water 17, no. 17: 2633. https://doi.org/10.3390/w17172633

APA Style

Błaszczyk, A., & Kobos, J. (2025). Toxic Potential and Long-Term Dynamics of Cyanobacterial Blooms in the Gulf of Gdańsk (Southern Baltic Sea). Water, 17(17), 2633. https://doi.org/10.3390/w17172633

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